Nonwoven fabrics have been around for many years and today there are a number of different nonwoven production technologies being used commercially. One important area of application for nonwoven fabrics is in the field of wiping materials, also known as “wipes” or “wipers”. Wipes are used for a large number of purposes in industrial, domestic, institutional and personal cleaning settings. Within these applications, a common requirement is that the wipe be absorbent towards water and aqueous solutions, or towards certain solvents in the case of industrial wipes. Wipes are often sold and packaged in a pre-moistened state as ‘wet wipes’. Other common requirements of wipes include the ability to remove and retain dirt, softness, bulk, and strength appropriate to the intended use, and a low propensity to lint (shed fibres and/or particles). When the wipe is intended to be used in the wet state, the aforementioned properties are usually measured as ‘wet properties’ after the nonwoven fabric has been suitably wetted. It is intended that many wipes be single-use (e.g. baby and personal hygiene wipes) or limited re-use articles (e.g. some types of kitchen wipes). Current trends in the field of consumer wipes (baby wipes, personal hygiene wipes, and domestic cleaning wipes including disinfection wipes), place emphasis on cleaning performance, economy, and concern for the environment. The consumer requires a high level of cleaning performance, that is, principally dirt removal whilst leaving little or no residual lint or streaks on the wiped surface. Reducing the basis weight of a wipe needed to perform a particular cleaning task will consume fewer raw materials per wipe, and will be more economical. The basis weight of baby and personal hygiene wet wipes is generally from about 40 gsm to about 65 gsm, and the basis weight of consumer domestic cleaning and disinfection wet wipes is generally from about 40 gsm to about 55 gsm. There is increasing public concern over the use of natural resources being utilised in the manufacture of wiping articles whose use is of limited duration. Hence there is growing consumer demand for wipes produced with less environmental impact, for example wipes made from a high percentage of renewable and sustainable materials, and preferably wipes which are biodegradable after use.
Woodpulp is used in various types of nonwoven fabrics made by different technologies. Although nonwoven fabrics made from woodpulp fibres are known to be absorbent, nonwoven fabrics made entirely of pulp fibres may be undesirable for certain wiping applications because they lack adequate strength and abrasion resistance, and are prone to shed pulp fibres during use. A wipe is often used to clean a surface by rubbing the wipe on the surface. The action of rubbing abrades the surface of the wipe. If the material used to make the wipe has a low resistance to abrasion, this results in the wipe having relatively poor durability and an excessive number of fibres or other particles are likely to detach from the wipe and contaminate the wiped surface. This is particularly the case when the wiping substrate contains woodpulp. In the past nonwoven fabrics with a high pulp content have been strengthened by either the application of chemical binders, and/or by using other bonding techniques such as hydro-entanglement. Each of these approaches has drawbacks. For example, the use of man-made chemical binder dispersions adds cost, generally increases energy consumption during manufacture due to the need for additional drying of the web, and may cause undesirable streaking when the wipe is used to clean a hard surface such as glass. Due to the short length of woodpulp fibres (generally less than 4 mm, and commonly about 2 mm), hydro-entanglement of 100% w/w woodpulp webs with high pressure water jets has only a limited effect. Generally longer fibres or filaments must be mixed with the pulp fibres, or otherwise provided, such that the woodpulp fibres can ‘wrap around’ the longer fibres or filaments during the hydro-entanglement process. Examples of the hydroentanglement of woodpulp fibres in the presence of longer fibres are disclosed in Canadian patent 841,938 and U.S. Pat. No. 5,009,747. Hydro-entanglement with high pressure water jets is a high energy process, and a further consequence is the densification of the nonwoven fabric, i.e. reduction of web thickness and bulk during hydroentanglement. High wood pulp content, hydro-entangled nonwoven fabrics may still lint to an unacceptable degree, and require further treatment such as addition of a chemical binder.
A number of meltspun technologies have been used to make nonwoven fabrics. Meltspun nonwovens can be made from a range of thermoplastic resins including (but not exclusively) polymers and/or copolymers of olefins, esters, amides, urethanes, and vinyl compounds such as vinyl chloride, vinyl alcohol, and vinyl acetate. The resin(s) may include those made from sustainable sources such as poly(lactic acid) and other plant derived thermoplastics. The spunbond process produces multiple, essentially continuous, polymer filaments which are laid on a moving foraminous surface to form a loose web, which is commonly then bonded by means of heated calender rolls. Spunbond webs are generally strong and porous. U.S. Pat. No. 3,802,817 describes the spunbond process and equipment. The meltblown process was first developed in the 1950's to provide advanced filtration materials, as described in Van A. Wente in Industrial and Engineering Chemistry, Volume 48, No. 8 (1956). U.S. Pat. Nos. 3,379,811, 3,634,573 and 3,849,241 describe the process. Meltblown webs are usually weaker than the equivalent weight spunbond web, but have smaller pores, and as such are often used in filtration applications. The two technologies can be combined to make composite fabrics such as the 3-layer spunbond-meltblown-spunbond, or ‘SMS’ composite fabric, which combines the strength of spunbond with the filtration capability of meltblown webs. The product of another hybrid technology is the so called high strength meltblown nonwoven whose method of manufacture is described in U.S. Pat. Nos. 4,731,215 and 6,013,223. Although the use of 100% w/w synthetic meltspun webs as wiping materials has been described in U.S. Pat. No. 6,315,114B1 and in US patent application 2005/133174A1, such wipes are more commonly used in professional and industrial applications rather than as consumer wipes. Meltspun webs have been combined with woodpulp, usually through hydro-entanglement, to make nonwovens suitable for use as wiping materials. U.S. Pat. Nos. 4,442,161, 4,808,467 and 4,939,016 describe such woodpulp-meltspun web composites.
Nonwoven technologies used today to make wiping materials with a high percentage woodpulp content include coform, airlaid and hydroentangled composites.
A coform nonwoven is a sheet material comprising an intimate blend of meltblown filaments (usually polypropylene filaments) and cellulose fibres (usually woodpulp fibres). In the coform process, woodpulp fibres (typically about 70% by weight of the fabric) are individualised, transported in an airstream which is combined with a second airstream carrying meltblown filaments. The combined airstreams deposit the fibrous materials on a foraminous surface. Coform-type processes and fabrics are described in U.S. Pat. Nos. 4,100,324 and 5,350,624. Coform nonwoven fabrics are usually bulky and soft, but generally have relatively poor wet abrasion resistance, resulting in a higher linting propensity.
In the airforming process, the woodpulp fibres (typically 70% or more by weight of the fabric) are individualised using, for example, a hammer mill, transported in an airstream to a distribution device which distributes the fibres substantially uniformly in the cross-direction of the production machine. After passing through the distribution device, the fibres are deposited on a foraminous moving surface by means of an airflow created by vacuum boxes below the surface. Other materials such as man-made fibres, powders or particulates may be mixed with the woodpulp fibres. The airformed web may be bonded by a number of methods including heat activated binders and/or application of liquid binders. U.S. Pat. No. 3,575,749 describes the airlaid process, and U.S. Pat. No. 4,494,278 describes a fibre distribution device used to make airformed webs. When airformed webs are used to make wiping substrates, the strength of the web is strengthened by spraying or otherwise applying a liquid binder, typically an aqueous synthetic latex dispersion, to one or both web surfaces which must then be dried and cured. By applying the liquid binder principally to the web surfaces, the detachment of fibres (also known as shedding or linting) from the surfaces of the substrate is reduced. A recent embodiment of the airlaid process for the production of wiping materials is the so called multi-bond airlaid (MBAL) process. In the MBAL process, thermoplastic binder fibres (typically about 30% by weight of the fabric) are blended with woodpulp fibres. The binder fibres are typically of a sheath: core bicomponent configuration, where the sheath polymer has a lower melting point than the polymer comprising the fibre core. After depositing the blend of woodpulp fibres and binder fibres on a foraminous surface to form a web, the web passes through an oven where the binder fibres bond to neighbouring fibres, thereby strengthening the web. Additionally a light application of a liquid binder, typically an aqueous synthetic latex dispersion, is applied to one or both surfaces of the web to reduce the number of fibres detaching during use as a wipe. Airlaid webs, including multi-bond airlaid webs, are usually bulky, can be soft depending on choice of binder(s), but have poor wet abrasion resistance, resulting in a higher linting propensity.
Hydro-entangled nonwoven composites of woodpulp and other fibres or filaments have long been known. U.S. Pat. Nos. 3,485,706 and 3,560,326 describe hydro-entangled composites of polyester staple fibres and woodpulp. U.S. Pat. Nos. 4,442,161 and 4,808,467 describe hydro-entangled composites of spunbond webs and woodpulp. Such nonwoven composites generally contain less than about 70% by weight woodpulp fibres. U.S. Pat. No. 5,284,703 describes a composite fabric made by hydro-entangling woodpulp into a spunbond web, and where the woodpulp content of the composite nonwoven is at least 70% by weight. Depending on the choice of raw materials, such woodpulp containing hydro-entangled webs may have good wet abrasion resistance, but are not very soft or bulky, and are typically used to make industrial or hard surface wipes.
Testing of commercial samples of wipes made from the aforementioned nonwoven technologies, demonstrates that they have either good wet abrasion resistance, or good wet bulk, or low linting propensity, but not all these desirable properties together. It is an object of the present invention to provide an improved nonwoven wiping material with the combination of good wet bulk, good wet abrasion resistance and with a low propensity for linting, and with a high woodpulp content of at least 50% by weight.